273 Impacts of commingling on health and productive responses of beef heifers during feedlot receiving

Abstract

Abstract This experiment compared physiological, health, and performance responses of beef heifers assigned to different commingling schemes (1, 2, or 4 sources/pen) during a 56-d feedlot receiving period. Ninety-six recently weaned Angus-influenced heifers were purchased from a commercial auction facility. Heifers originated from 4 cow-calf ranches, and were reared in the same herd within each ranch since birth. Heifers were loaded by source into commercial livestock trailers at the auction yard, and transported for 8 h to stimulate the stress of a long haul. Heifers were not mixed with cohorts from other sources prior to and at the auction yard. Upon arrival at the receiving yard (d -2), shrunk body weight (BW) was recorded, and heifers were maintained in 4 paddocks by source with ad libitum access to hay, water, and a mineral supplement for 36 h. On d 0, heifers were ranked by source and shrunk BW and allocated to 1 of 24 drylot pens (4 heifers/pen) containing: 1) heifers from a single source (NOCOM, n = 8 pens), 2) heifers from 2 sources (COM2, n = 8 pens), or 3) heifers from 4 sources (COM4, n = 8 pens). From d 0 to 55, heifers had free-choice access to water and a total-mixed ration. Heifers were assessed for bovine respiratory disease (BRD) signs and feed intake was recorded from each pen daily. Blood samples were collected from all heifers on d 0, 6, 13, 27, 41, and 55, and shrunk BW (after 16 h of water and feed withdrawal) was collected on d 56 for average daily gain (ADG) calculation. Final shrunk BW and ADG did not differ (P ≥ 0.83) between NOCOM, COM2, and COM4 heifers (0.85, 0.88, and 0.82 kg/d of ADG, respectively, SEM = 0.08). No treatment effects were detected (P ≥ 0.77) for feed intake and feed efficiency, as well as plasma concentrations of haptoglobin and cortisol. No treatment differences were noted (P ≥ 0.49) for morbidity (53.1, 68.7, and 56.2% of NOCOM, COM2, and COM4 heifers diagnosed with BRD, respectively; SEM = 9.7) or mortality during the experiment. A similar (P ≥ 0.97) proportion of NOCOM, COM2, and COM4 heifers diagnosed with BRD required at least two treatments to recover from sickness. In turn, a third treatment was not required for NOCOM heifers, which was less compared with COM4 (P = 0.05) and similar (P = 0.23) compared with COM2 heifers. Perhaps the number of heifers assigned to commingled pens, and resultant pre-existing social groups, was not sufficient to stimulate the stress reactions caused by social destabilization.